PHP4 also have reference count feature. For example, memory for variables is shared when it assigned to other variable. If contents has been changed, PHP4 allocate new memory for it.

For example, programmer does not have to use pass by reference for large parameters for better performance with PHP4.

It would be a nice section for new PHP users, if there is "Resource Handling" section or like. Explanation about reference count feature in PHP4 would be very helpful to write better PHP4 scripts also.